g to the glands and the
vascular system might betray great tension, not so much by movements as
by a flow of perspiration (we have many excellent examples of this given
by Manouvrier)[93] or by a violent beating of the heart, blushing and
the like,--in short, by secretory and vasomotor effects. Or it is not
inconceivable that long dealing with very abstract thoughts might have
weakened the tendency of overflow to other parts of the brain, and that
therefore the entire discharge is used up in those portions of the brain
which are the basis of the intellectual processes. But if expressive
movements occur, the motor pathways must be particularly unresisting in
order to take up the overflow of psychophysic energy. This is the
necessary condition for obtaining the tapping and the head movements on
the part of the horse, although for the tapping there is still one other
circumstance necessary: viz.,

4. The power to distribute tension economically--i. e., the ability to
sustain it long enough, and to release it at the right moment (after the
manner of the curves described on page 93), and to control properly the
unavoidable variations which will occur.[AI]

[Footnote AI: The mental state just described is probably
essentially the same as that of the spiritualistic "mediums" when
they are occupied with table-rapping and table-moving. In both cases
concentration is very intense,----in other words, the field of
attention is limited. We saw that this state not only favors the
tendency toward involuntary movement, but on account of the
absorption of the individual's attention by a certain limited
content, the person will be unaware of the voluntary movements as
they occur. And we are not necessarily here dealing with
neurasthenic, hysteric, or other diseased nervous conditions. In the
case of table-rapping there are movements of the hands, in our case
there are those of the head. Our head, balanced as it is upon the
cervical vertebral column, is continually in a state of unstable
equilibrium and therefore peculiarly susceptible to
movement-impulses of every kind. But I could induce not only
movements of the head, but also of the arms and legs, and this by
having the subject assume a posture which enabled him to hold arms
or legs in as unstable a position as possible. He might stretch out
his legs horizontally before him, or he could raise them vertically